Question: I am writing a story with two main characters. This whole story (which I am writing in 4 parts/books) spans roughly eight years. The characters do not meet one another until two years into the story. One of the characters has substantial development in the first two years, while the latter character has very minimal development. I don't want the story to be one-sided for the first bit of the story. The second character also seems really bland and static. Any ideas on how to put this character into situation(s) that will develop her independently of the first character?
The important thing is that you show both characters coping with a problem in their unique way, so that the reader gets to understand how these characters think and act, their respective situations and natures. The resolutions of these problems should be events -- significant changes that open up new possibilities for each character. (Later, as the story progresses the characters can be pressured to change their approach, creating inner conflict.)
We understand characters when we see them in action, coping with problems that are serious to them and which we can empathize.
It doesn't matter how many pages each of these events take up, so long as they fulfill their task. In other words, it's okay if one character gets more pages in the beginning so long as their opening events are equally significant.
Even if these characters don't meet, you might also consider giving some hint that their stories are or will be connected. Do they know some of the same people, live in the same community, etc.? Do they actually pass each other on the street without meeting?